NAME

Box2D::b2Manifold - Manifold for two touching convex shapes.

SYNOPSIS

  my $manifold = $contact->GetManifold();
  my $normal = $manifold->localNormal();
  my $point = $manifold->localPoint();

DESCRIPTION

A manifold for two touching convex shapes.

Box2D supports multiple types of contact:

clip point versus plane with radius
point versus point with radius (circles)

The local point usage depends on the manifold type:

e_circles: the local center of circleA
e_faceA: the center of faceA
e_faceB: the center of faceB

Similarly the local normal usage:

e_circles: not used
e_faceA: the normal on polygonA
e_faceB: the normal on polygonB

We store contacts in this way so that position correction can account for movement, which is critical for continuous physics. All contact scenarios must be expressed in one of these types. This structure is stored across time steps, so we keep it small.